1. Field of the Invention
The invention relates to the field of printing systems and in particular relates to improved systems and methods for sheetside dispatch in high speed printing systems using a clustered computing printer controller.
2. Discussion of Related Art
In high performance printing systems, which can be continuous form printing systems or cut sheet printing systems, the image marking engines apply RIPped (e.g., rasterized) images to continuous form paper moving through the marking engine at high rates of speed. Typically, pages to be imaged are combined into logical “sheetsides” that consist of one or more pages of equal length which when laid out for printing, span the width of the print web. Bitmap images of each sheetside to be printed are generated (RIPped) by a printer controller coupled to the high speed printing engine. It is vital in such high performance printing systems that the printer controller generates required bitmaps rapidly enough to maintain continuous throughput of paper through the image marking engine.
Two undesirable situations can occur when sheetsides cannot be ripped fast enough to feed the printer at a specified speed. First, the printer may slow its print speed as the quantity of ripped sheetsides ready to be printed decreases, thus causing a decrease in print throughput. This situation can happen in both continuous form and cut sheet printers. Secondly, in continuous form systems, the high speed marking engine may be forced to stop imprinting, stop the continuous form feed, and then restart at some later time when some predetermined quantity of ripped sheetsides is available for print. This type of event is known as a “backhitch”. Not only does backhitching cause reduced print throughput, it can also result in undesirable print quality or tearing of the print web due to the abrupt stoppage of the paper. If the print web is torn, even more time is consumed in recovering from such an event.
In higher volume printing system environments such as high volume transaction or production printing (e.g., consumer billing statements, payroll processing, government printing facilities, etc.) such wasted time in a slower than planned print speed or a backhitch operation can represent a substantial cost to the printing environment. Downtime in such high volume printing environments is a serious problem for which printing system manufactures expend significant engineering effort to resolve. These problems are further exacerbated in two sided or duplex printing operations where the continuous form paper is fed through a first image marking engine, physically turned over, and fed in a continuous form fashion through a second image marking engine for printing the opposing side of the medium. Stopping such printing systems and performing a backhitch operation to accurately position the paper in multiple image marking engines further complicates the problems. Further, the processing workload for the printer controller in generating bitmap images for duplex printing is approximately twice that of simplex or single sided printing processing.
It is generally known to provide additional computational processing power within the printer controller to help assure that required bitmaps will be ready in time for the image marking engine to avoid the need for time consuming stop and backhitch operations. One recently proposed improvement teaches the use of a cluster computing architecture for a printer controller wherein multiple computers/processors (“compute nodes”) are tightly coupled in a multiprocessor computing architecture. The aggregated computational processing power of the clustered computers provides sufficient processing capability in hopes of assuring that a next required bitmap image will always be available for the image marking engines.
Despite the presence of substantial computational power even in a clustered computing environment, there is a need to optimize the scheduling dispatch of sheetside bitmap image processing (“ripping”) on the multiple compute nodes in the cluster in order to produce an efficient and cost-effective system. Well-known simplistic scheduling algorithms fail to adequately ensure that a next required bitmap will likely be available when required by the marking engines. Use of such simplistic algorithms also typically results in the need to specify more compute nodes than would be necessary under most circumstances, resulting in a more expensive system.
It is evident from the above discussion that a need exists for an improved method and associated systems for scheduling dispatch of sheetside bitmap image processing (e.g., RIPping) among the plurality of processors in a multi-computer clustered print controller environment to help reduce the possibility of image marking engine slowdown, or stoppage and backhitch.